A standard printer has an ink-transfer or anilox roll that is fed ink from a supply cartridge that sits atop the transfer roll and that fits tightly with the roll so that a body of ink held in the supply sits atop the roll. Such a supply has a pair of doctor blades that have outer edges that engage the roll along lines parallel to the axis thereof, with the space between these lines forming a downwardly open ink-feed mouth. As the roll rotates, its surface is wetted, and excess ink is scraped off the roll by the downstream doctor blade.
In order to change the supply or roll, it is standard as described in U.S. Pat. No. 7,234,396 to make one of the doctor blades movable and couple it to a mechanism that allows it to be shifted from an open position with its outer edge spaced from the outer edge of the other doctor blade to a closed position with its outer edge engaging the other blade and closing the mouth. When thus closed the supply and roll can be separated while the supply continues to hold a body of ink.
The ink supply typically has a frame-like shape with two short opposing end plates and two opposing long side plates, the latter extending parallel to the roll axis. Each side plate carries a respective doctor blade. Optionally, one side plate can directly form a doctor blade.
In order to apply ink, the two outer edges of the doctor blades are prestressed radially inward against the ink-transfer roll so that a rolling ink body is formed by the rotation of the ink-transfer roll against the downstream doctor blade, and the ink is transferred from this ink body onto the ink-transfer roller. The upstream doctor blade opposite the downstream doctor blade essentially functions here to seal the opening of the ink supply relative to the ink-transfer roll when the ink-transfer roll is stationary, i.e. when the ink located in the ink supply is completely distributed within the ink supply.
Frequently a change must be made in a printing machine or unit from one ink to another ink, meaning that either the corresponding ink cartridge must be completely emptied and cleaned, which entails a significant labor-intensive and time-intensive effort for the machine, or, on the other hand, an ink cartridge including the ink contained in the ink cartridge must be switched with another.
Changing an ink cartridge presents a problem, particularly when printing ink is left in the ink cartridge, since this ink runs out through the opening of the ink cartridge between the two edges of the doctor blades onto the ink-transfer roll when the ink cartridge is lifted off the ink-transfer roll, and possibly onto other internal elements of a printer, thereby contaminating the machine.
In order to avoid these problems, the approach known in the art is either to completely drain an ink cartridge before changing it, or before the change to have a service person remove the ink remaining in the ink cartridge manually or to remove it by a controlled suction device. However, this procedure is labor-intensive and time-intensive, in particular whenever the ink cartridge is still almost completely filled.
Another approach known in the art is as described above to design ink supplies such that the opening between the doctor blades can be closed toward the ink-transfer roll, where provision is made whereby the ink along with an ink module, i.e. a cartridge matched to the interior of the ink cartridge is introduced into the ink cartridge, the container being first closed toward the ink-transfer roll by means of an additional closure plate.
In operation, this plate is removed and the ink is able to pass to the ink-transfer roll. Whenever the ink needs to be switched, this plate is re-introduced and closes the opening to the ink-transfer roll, thereby allowing the ink module together with the ink therein to be removed. A disadvantageous aspect of the described approach is the fact that the printing ink that passes during normal operation onto the doctor blades remains there during removal of the ink module, and ink also continues to pass between ink module and ink cartridge, with the result that both the outer area of the ink module after removal and the now inner area of the ink cartridge have to be cleaned.
In addition, an increased amount of ink remains on the ink-transfer roll in the area of the opening of the ink cartridge facing the ink-transfer roll since the additional module plate runs in guide grooves in the ink module and as a result the ink-transfer roll cannot be wiped off. This also disadvantageously results in an increased cleaning cost for the ink-transfer roll itself and, in particular, in an associated high ink consumption when the ink is changed frequently.
Another approach is known in the art whereby the ink cartridge is closed toward the ink-transfer roll by a doctor blade that is attached to a doctor bar and is movable along with the doctor bar, wherein the doctor bar is moved along with the doctor blade attached thereto onto the opposing doctor blade. This type of ink cartridge is revealed, e.g. in U.S. Pat. No. 7,234,396. What is disadvantageous about this type of closure is that the compartment volume of the ink cartridge is significantly diminished by the displacement of the doctor bar together with the doctor blade, such that there is a risk of overflow, particularly when the ink cartridge is filled completely or almost completely, thereby causing printing ink to pass in uncontrolled fashion into the printer. What is furthermore disadvantageous is the fact that before this type of ink cartridge is removed from a holder of a printer the service personnel must ensure that the ink cartridge is closed tightly. Otherwise ink will accidentally discharge from the ink cartridge during the removal operation.